The gender would be easier to tell by looking at the combs and wattles. My RIR pullets are 8 wks. old and some of them have shorter tail feathers than some of the other ones. Try posting some pics, the breed of the chicken and maybe everyone can better help you out with the gender.

Im still learning this but I think in the 9th picture the 2 in focus could be roos, the rest to me seem like pullets! Good Luck! Very pretty birds.
Well the 2 with the back of their heads towards the camera.

It's been too long since I've raised RIR's, but for your orpington's they're easy to tell at 6 weeks if you look at the combs and waddles.

For instance, looking at the picture stamped 11 4:53PM the three in the center and foreground are males (including the black) and the two buff orps behind them (one facing left and the other facing right with that "what are you up too expression") are pullets.

With our orps the combs are twice as big on the males and they have larger leg muscles and slightly more pronounced waddles.